1. Field of the Invention
The present invention relates to a new method for synthesizing crystalline molecular sieves using a family of templating agents.
2. Background
The crystalline materials of this invention contain metallic and non-metallic oxides bonded through oxygen linkages to form a three-dimensional structure. Molecular sieves are a commercially important class of crystalline materials. Natural and synthetic crystalline molecular sieves are useful as catalysts and adsorbents. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species. The adsorptive and catalytic properties of each molecular sieve are determined in part by the dimensions of its pores and cavities. Thus, the utility of a particular molecular sieve in a particular application depends at least partly on its crystal structure.
Because of their unique sieving characteristics, as well as their catalytic properties, molecular sieves are especially useful in such applications as gas drying and separation and hydrocarbon conversion. Although many different molecular sieves have been disclosed, there is a continuing need for new materials with desirable properties for gas separation and drying, hydrocarbon and chemical conversions, and other applications.
Aluminophosphate molecular sieves containing AlO.sub.2 ! and PO.sub.2 ! units have been disclosed in U.S. Pat. No. 4,310,440, issued Jan. 12, 1982 to Wilson et al. Silicoaluminophosphates having a three-dimensional crystal framework of PO.sub.2.sup.+, AlO.sub.2.sup.- and SiO.sub.2 tetrahedral units are taught in U.S. Pat. No. 4,440,871, issued Apr. 3, 1984 to Lok et al. Aluminophosphates containing AlO.sub.2 ! and PO.sub.2 ! structural units, and one or more metals in tetrahedral coordination with oxygen atoms are disclosed in U.S. Pat. No. 4,567,029, issued Jan. 28, 1986 to Wilson et al. The '029 reference teaches using the metals magnesium, manganese, zinc, and cobalt, and uses the nomenclature "MeAPO" to identify these metal aluminophosphate materials. U.S. Pat. No. 4,686,093, issued Aug. 11, 1987 to Flanigen et al., describes aluminophosphates containing at least two elements selected from arsenic, beryllium, boron, chromium, gallium, germanium, lithium and vanadium. U.S. Pat. No. 4,913,799, issued Apr. 3, 1990 to Gortsema et al., discloses a large number of aluminophosphates for use in hydrocracking processes. The aluminophosphates of '799 contain AlO.sub.2 ! and PO.sub.2 ! structural units, and one or more metals in tetrahedral coordination, including arsenic, beryllium, boron, chromium, cobalt, gallium, germanium, iron, lithium, magnesium, manganese, silicon, titanium, vanadium, and zinc. U.S. Pat. No. 4,973,785, issued Nov. 27, 1990 to Lok et al., expands the list of aluminophosphates, and teaches the use for converting hydrocarbons using silicoaluminophosphates containing at least one element, "EL" capable of forming a three dimensional oxide framework having a mean "EL--O" distance in tetrahedral oxide structures between 1.51 .ANG. and 2.06 .ANG., where "EL" has a cation electronegativity between 125 to 310 kcal/g-atom, and is capable of forming stable EL--O--P, EL--O--Al or El--O--El bonds in crystalline three dimensional oxide structures having an "EL--O" bond dissociation energy greater than about 59 kcal/mole at 289.degree. C.
Organic templating agents are believed to play an important role in the process of molecular sieve crystallization. Organic amines and quaternary ammonium cations were first used in the synthesis of zeolites in the early 1960's. This approach led to a significant increase in the number of new zeolitic structures discovered as well as an expansion in the boundaries of composition of the resultant crystalline products.
Unfortunately, the relationship between structure of the organocation and the resultant zeolite is far from predictable, as evidenced by the multitude of products which can be obtained using a single quaternary ammonium salt as reported by S. I. Zones et al., 1989, Zeolites: Facts, Figures, Future, ed. P. A. Jacobs and R. A. van Santen, pp. 299-309, Amsterdam: Elsevier Science Publishers., or the multitude of organocations which can produce a single zeolitic product as reported by R. M. Barter, 1989, Zeolite Synthesis, ACS Symposium 398, ed. M. L. Occelli and H. E. Robson, pp. 11-27, American Chemical Society.
Thus, it is known that organocations exert influence on the molecular sieve crystallization processes in many unpredictable ways. Aside from acting in a templating role, the organic cation's presence also greatly affects the characteristics of the gel. These effects can range from modifying the gel pH to altering the interactions of the various components via changes in hydration (and thus solubilities of reagents) and other physical properties of the gel. Accordingly, investigators have now begun to consider how the presence of a particular quaternary ammonium salt influences many of these gel Characteristics in order to determine more rigorously how such salts exert their templating effects.
It has been noted that many of the organocations which have been used as templates for zeolite synthesis are conformationally flexible. Thesemolecules can adopt many conformations in aqueous solution, therefore several templates can give rise to a particular crystalline product. Studies which involved alterations on such conformationally flexible organic amines and cations have been published. For example, one study, Rollmann and Valyocsik, 1985, Zeolites 5, 123, describes how varying the chain length for a series of .alpha.,.omega.-linear diamines resulted in different intermediate-pore products. It has also been recently reported by M. D. Shannon et al., 1991, Nature 353, 417-420 and J. L. Casci, 1986, New Developments in Zeolite Science and Technology, ed. Y. Murakami et al., pp. 215-222, Elsevier that three different-products which have related framework topologies., can be formed from three linear his-quaternary ammonium templates of varying chain lengths.
Altering the structure of a conformationally rigid organic molecule can also lead to a change in the zeolite obtained, presumably due to the differing steric demands of each template. S. I. Zones, 1989, Zeolites 9, 458-467 reported that in switching from 1,3-dimethylimidazolium hydroxide to 1,3-diisopropylimidazolium hydroxide as template, using the same starting gel (SiO.sub.2 /Al.sub.2 O.sub.3 =100), the former directs toward formation of ZSM-22 whereas the latter affords ZSM-23.
In summary, a variety of templates have been used to synthesize a variety of molecular sieves, including zeolites, aluminophosphates, and silicoaluminophosphates.
Though the specific utility of a given template is at present unpredictable, a few notable cyclic-organocation templating agents have been reported. For instance, use of N,N,N-trimethyl cyclopentylammonium iodide in the preparation of Zeolite SSZ-15 molecular sieve is disclosed in U.S. Pat. No. 4,610,854, issued Sep. 9, 1986 to Zones; use of 1-azoniaspiro 4.4! nonyl bromide and preparation of a molecular sieve termed "Losod" is disclosed in Hel. Chim. Acta (1974), Vol. 57, page 1533 (W. Sieber and W. M. Meier); use of 1,.omega.-di(1-azoniabicyclo 2.2.2.! octane) lower alkyl compounds in the preparation of Zeolite SSZ-16 molecular sieve is disclosed in U.S. Pat. No. 4,508,837, issued Apr. 2, 1985 to Zones; use of N,N,N-trialkyl-1 adamantammonium salts in the preparation of zeolite SSZ-13 molecular sieve is disclosed in U.S. Pat. No. 4,544,538, issued Oct. 1, 1985 to Zones. U.S. Pat. No. 5,053,373, issued Oct. 1, 1991 to Zones discloses preparing SSZ-32 with an N-lower alkyl-N'-isopropyl-imidazolium cation templating agent. U.S. Pat. No. 5,106,801, issued Apr. 21, 1992 to Zones et al. discloses a cyclic quaternary ammonium ion, and specifically a tricyclodecane quaternary ammonium ion, for the preparation of the metallosilicate zeolite SSZ-31. U.S. Pat. No. 4,910,006, issued March 20, 1990 to Zones et al., teaches using a hexamethyl 4.3.3.0!propellane-8,11-diammonium cation for the preparation of SSZ-26. EP 0193282 discloses a tropinium cation for preparing the clathrasil ZSM-58. Similarly, use of quinuclidinium compounds to prepare a zeolite termed "NU-3" is disclosed in European Patent Publication No. 40016.
The use of 1,4-diazabicyclo 2,2,2!octane; N,N'-dimethyl-1,4 diazabicyclo 2,2,2!octane dihydroxide; and quinuclidine are examples of amines taught in U.S. Pat. No. 4,310,440, issued January 12, 1982 to Wilson et al., and U.S. Pat. No. 4,440,871, issued Apr. 3, 1984 to Lok et al. for the preparation of aluminophosphates and silicoaluminophosphates respectively.